Ultrahigh frequency marker beacon system



July 26, 1938, c. D. BARBULESCO ULTRAHIGH FREQUENCY MARKER BEACON SYSTEM Filed Feb. 4, 1935 4 Sheets-Sheet l INVENTOR L 501v; /V7'//V 0.54 045860 TTOR/VE Y5 Jill 26,1938.

c. D. BARBULESCO ULTRAHIGH FREQUENCY MARKER BEACON SYSTEM Filed Feb. 4, 1955 4 Sheets-Sheet 2 INVENTOR Co/vs 774 274 2 124R5JL6C0 July '26, 1938. c. D. BARBULESCO ULTRAHIGH FREQUENCY MARKER BEACON SYSTEM -Filed Feb. 4, 19:55 4 Sheets-Sheet s INVENTOR July 26, 1938.

C. D. BARB ULESCO ULTRAHIGH FREQUENCY MARKER BEACON SYSTEM Filed Feb. 4, 1935 4 Sheets-Sheet 4 IN V EN TOR 4 ORA 75 plane of the polarization of the energy inthe' iiiliGH FREQUENCY ".7 1".

% BEACON (Granted under the act or March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and usedby or for the Government for governmental purposes, without the payment to me of any royalty thereon.

My invention relates generally to a novel method of and means for transmitting'and receiving radiant energy and more particularly for transmitting and receiving electromagnetic energy of ultra-high frequency as an aid to the navigation of vehicles either on the ground, in the air, on the water, or under the water, and as an aid in the prevention of collision of such ve-.

hicles either among themselves-or against obstacles.

The principle of my invention will be readily understood when it is remembered that the electromagnetic waves of very short length are very similar to light, the difl'erence being that they do not aflect any of the human senses and therefore a receptor is needed to make their presence known.

My invention has for one of its objects to provide a simple, eflicient and economical ultrahigh frequency signalling systemJ Another object of my invention is to associate a. projecting means for bundling radiant energy of ultra-high frequency with a directional receiving means in such a manner that the presence of such radiant energy is detected in accordance with a predetermined virtual beam.

A further object of my invention is to provide a novel receiving means that is directionally responsive to an existing projected beam of radiant energy in accordance with predetermined relative displacements of said receiving means and the said beam.

Another object of my invention is to provide a. novel ultra-high frequency projector that will radiate in space a well defined beam of electromagnetic energy that is constant in. frequency, form and spread,

A further object of my invention is to provide a novel indicating means adapted to cooperate with a radio receptor and having novel means for signaling in response to the received electromagnetic energy to which the receptor is tuned.

A still further object of my invention is to pro vide a novel combination of ultra-high frequency projecting and receiving means having directional characteristics in predetermined relation for producing in space virtual beams of desired characteristics as a function of said relation and as a function of their relative displace- A still further object of my invention is to proand ultra-high frequency electro-magnetic energy.

A still further object of my invention is to provide a more efiicient amplification and detecting means for high and ultra-high frequency electromagnetic energy.

A further object of my invention is to associate a doublet antenna with an oscillator or detector in such a manner that the freedom of oscillation of said antenna is unrestrained by the presence of its associated circuit.

A still further object of my invention is to provide a novel arrangement of doublet antenna and a vacuum tube detector in which -the input and output circuits of said detectorare symmetrically connected to said doublet so that oscillations are simultaneously impressed upon the grid and plate that are substantially 180 out of phase.

The invention, as herein illustrated, is described in connection with the navigation and landing of aircraft under conditions of poor visibility when it is necessary to locate with great precision known geographical positions along the course of the aircraft or along its gliding path in negotiating a blind landing.

Fig. 1 is a front elevational view of the projector embodying my invention.

Fig. 2 is a diagrammatic view showing the circuit arrangements within the projector shown in Fig. 1, the physical structure being shown in phantom. x

Fig. 3 is a-modification of the circuit shown in Fig. 2.

Figs. 4 and 5 are respectively front and side elevational views of the field patterns produced by a doublet antenna.

Figs.6 and 7 show respectively front and side elevationsof field patterns when a doublet antefnna. is arranged in accordance with my invention.

Figs. 8 and 9 show field patterns of the actual and virtual beams in solid and dotted lines respectively for the novel combination of doublet antennae relationship.

Fig. 10 is a circuit diagram of the receptor device. e

Figs. 11 and 12 are schematic diagrams of an Fig. 15 is a circuit diagram of a further embodiment of my invention.

generates the oscillations.

Fig. 16 is a circuit diagram of a practical embodiment of my invention.

Fig. 17 is a longitudinal sectional View of a receptor device embodying my invention.

Fig. 18 is a cross-section taken'on the line 08-48 of Fig. 17.

Fig. 19 is an assembly view of the constituent parts of the receptor circuit system.

Fig. 20 is a side elevational view of an airplane to which the receptor circuit system is applied.

The signalling system embodying my invention comprises a projecting means, a receiving means and an indicating means.

The projecting means, comprises a generator of ultra-high frequency A, a radiating means B, a power converter C and a source of supply D.

the doublet remain. undisturbed. In other words, the shield by-passes the middle portion of the antenna current and constitutes the middle portion of the doublet. Asin the center of the doublet, the voltage is zero, the shield can be grounded, and practically is grounded, through the metal column 22 and the lower case.

The converter consists of a motor generator 26 and a transformer 25 having a primary winding 25, a secondary winding 21. for the filament, and another secondary 28 for the plate. The projector illustrated herein is especially designed for field operation and therefore raw alternating current of low frequency, such as 60 cycles, which is readily available, is supplied to both plate and filament from the alternator 29 driven by the The projecting means, as shown in Figs. 1 and 2, is arranged as a portable unit. This unit comprises a removable head that constitutes a casing for a generating means 'A and isdetachably connected to a column, which in turn is fixedly attached to a base. Projecting from opposite sides of the head and insulated therefrom are rigid arms made of copper or aluminum tubing that constitute with the head a doublet antenna B, as will be hereinafter described. The generating means is connected through a power line to'a converter 0 that is disposed within the base. Power is supplied to the converter from a source of supply such'as a heavy battery D.

The generating means comprises a constant frequency oscillating circuit as shown in Fig. 3. The principle of operation of the circuit is described in my Patent No. 1,874,222.

A vacuum .tube having a filament l, a grid 2 and a plate 3 in an evacuated glass container 4 A grid condenser 5 associated with a grid leak or grid resistor 6 produces the proper bias on the grid of the oscillating tube. A tank circuit comprising a large condenser I and a small inductance 8 is connected across the grid and theplate of the tube. A blocking condenser I of large value prevents the passage of direct current. The choke coils 9, l0, H and I2 insulate the ultra-high frequency oscillations from the sources of power l3 and I4,

which are at ground potential. The ultra-high motor 30, which derives its power from the battery D.

The antenna B is normally disposed in a horizontal position at a height of a quarter wave above the ground surface or any suitable metallic reflector. This arrangement permits the elimination of the choke coils 9, II and I2, and therefore a simplification of the circuit. Thisis pos-'- sible due to the fact that the leads to the filament are quarter wave long and constitute the most perfect choke for the; frequency at which the oscillator is operated. ,4

A by-pass condenser 3| is shunted across the secondary 28 of the transformer 25, lowering the impedance of the plate circuit and thus facilitating the oscillations. v

The radiation of the antenna is indicated by a high frequency ammeter 32 inserted in the cenfrequency energy is transferred from the tank circuit into a loading coil I5 inserted in the middle of a doublet antenna l6 and I1.

In order to prevent asymmetry in the distribution of the current and voltage along the doublet,

the grid and plate of the oscillating tube are maintained at equal, high frequency potentials with respect to the middle point of the coil 8,

which assumes ground potential and coincides with the nodal point of the doublet.

Referring to Fig. 2, wherein a practical realization of the projector is shown, it will be seen that the oscillatory circuit proper is enclosed in the metallic, head l8, which shields the oscillator circult and prevents the direct radiation of coil 8 'to interfere with the normal radiation of thedoublet antenna. As heretofore noted, the two sides It and ll of the antenna are brought out of the shield through two insulators 28 and 2|. Substantial capacitance, however, is provided.

between the shield and the antenna through theinsulators to permit capacitive coupling between the antenna and the shield. This is done for shield from the loading coil l5 so'that the sinusoidal distribution of voltage and current in equatorial plane is as respectively.

ter of the doublet and mounted in the head. An alternating current voltmeter 33 is shunted across the filament terminals and a direct cur-. rent milliammeter 34 is in the plate circuit return to indicate the emission ofthe ztube. These indicators are mounted in. the lower housing 23.

At extremely high frequencies eventhe con denser 1 can be dispensed withbecause the distributed capacity ofthe coil 8 and the interelectrode capacity between plate and grid in parallel, are sumciently large for the tank circuit. In this case the tuning within narrow limits can be accomplished by the grid condenser 5', which is made variable.

The distribution of voltage and current in the doublet are respectively represented by the curves a and b in Fig. 4. If the doublet in isolated in space far from reflecting surfaces the pattern of the radiated field in its own plane: and in the shown in Figs. 4 and 5 In any plane ofthe antenna the field from the center'in different directions varies with the angle in accordance with the formula:

cos ces a) sin 0:

Where E is the electric field, lVI the magnetic field and I0 the current at the center of the antenna, it is maximum for o t=% and zero for =o.

distances from the center, as shown in Fig. 5. the purpose of diverting enough current into the When the doublet is disposed. at adistance of a quarter wave above the surface of the ground G or any reflecting surface, reflection takes place and a field pattern is produced of a character as shown in Figs. 6 and 7. In the zenithal direction of the center of theantenna the field is reinforced because the reflected energy is in phase with the energy radiated directly by the antenna. The field pattern discloses a fan-shaped beam with the plane of the fan perpendicular to the direction of the antenna.

The receiving circuit, as illustrated in Fig. 10, is similar to the constantfrequency circuit used in the transmitter and is employed where the carrier frequency is modulated. This circuit comprises a vacuum tube having a filament 35, a

grid 31, and a plate 38 in an evacuated glass container 39.

A tank circuit having a large capacity 40 and small inductance 4| is connected between said plate and grid. The proper bias on the grid is 'produced by the grid condenser 42 and the grid resistor 43. A blocking condenser 43' insulates the tank circuit from the direct current plate voltage. A plurality of choke coils 44, 45, 46 and 41 prevent the leakage of the high frequency induced in the tank circuits into the sources of supply 48 and 49, which are maintained at ground v potential.

A doublet having a loading coil 50 is inductively coupled to the tank circuit. The two halves i and 52 of the doublet will absorb energy from the field and transfer it to the tank circuit, which is tuned exactly to the frequency of the energy voltage for which the gaseous discharge starts.

After detection the audio component builds suflicient additional alternating voltage across the transformer to flash the neon tube.

Where a more striking signal is needed as, for example, to warn a pilot of an airplane in effecting a blind flight, I prefer to employ a difierent type of indicating means. I have spent considerable time in developing sensitive relays to operate on the output of the detector to close a local circuit for flashing a light on the instrument board. I found that the energy after detection is exceedingly small and that the sensitive relays required for this purpose were readily upset by the vibration of the airplane. In order, therefore, to produce a flash of light with the minute amount of energy available I have associated a direct current meter with the detector circuit and with a single lighting circuitin such manner that while each operates independently of the other the efiect of the latter is not made known until the former is in operation.

This indicating means comprises a well-known A. C. converting circuit that is connected across -the terminals of a secondary 58 of the trans-.-

former 54 and a direct current meter L that is provided with a light bulb 60, the lightlrays of which are observed when the needle of the meter is actuated away from its zero position.

A preferred embodiment of the meter and bulb arrangement is shown on Figs. 13 and 14, wherein the bulb 50 is shown mounted between suitable spring contacts and arranged at one end of a bent glass rod H. The other end of the rod is disposed immediately behind an opening 52 formed in the card 63, which opening is normally maintained shut by means of a disk 61 carried by the pointer 65. It will be seen that when the alternating current component in the plate circuit of the detector is rectified by the contact-type rectifier 56, the needle 65 will be actuated, thus uncovering the opening 62 and the-light rays will be projected therethrough to thereby produce a light flash signal. The size of the light opening may be varied by means of an adjustable disk 61' having a series of openings of different size. It will be noted that the light bulb is inserted into the meter case from the front side thereof through an opening that is covered by a cap 68. This will facilitate replacement oi bulb when necessary.

A variation of the arrangement of the bulb is shown in Fig. 12, wherein reflecting surfaces 69 and are used instead of the bent rod H. t

A more simple form of bulb arrangement is shown in Fig. 11, wherein the light bulb is disposed'immediately behind the opening, thus light rays are projected directly from the bulb through the opening.

In Fig. a simple crystal detector 12 is used in series with a by-passcondenser 13 connected symmetrically acrom the central portion of the doublet antenna. The indicator L" is connected acrossthe condenser 13. This novel arrangement will not interfere with the natural mode of vibration of the doublet and will not introduce any resistance in the antenna circuit.

Between the points 14 and '5 a high frequency voltage is developed by the-electromotive force induced in the antenna by the field. This voltage produces a current in the detector circuit 12 which is rectified and charges the condenser 13, which in turn become a source of direct current for actuating the indicator L". This arrangement will operate on a modulated or unmodulated carrier and finds practical application as an auxiliary inexpensive means of marking the boundary of a landing field or thecenter of the field by flashing a red light that is disposed within indicator L". The sensitivity of the arrangement just described is obviously small and I prefer to use it-i'or low altitudes or small distances.

For higher altitudes I prefer a vacuum tube detector of high sensitivity, as illustrated in Fig.

, 16. In this view, a vacuum tube 76 of the screen grid type is shown. The filament is of the heater type, having a filament proper or heater 1! and a cathode l8 heated indirectly by the said heater. The grid 19 and the plate 80 are directly connect- .ed respectively to the ends of the two halves 5| and 52 of the doublet antenna H. a

The screen electrode 80' is interposed betweer the said grid and plate and decreases the capacity between these electrodes. 1

A plurality of choke coils 8!, 82 and 83 insulate all the electrodes of the tube from the ground by preventing leakage of the high frequency intercepted by the antenna and transferred to said electrode. The grid leak 84 produces a suitable bias on the grid, while the blocking condenser 85 insulates the antenna 5| from the highvoltage applied tothe plate.- Two resistors 86 and 81 are used for cutting down the voltage of the filament battery N to the proper value needed by the filament. The plate battery M energizes the plate 80 and the screen grid 80'. A resistor 88, shunted in normal position by the test switch 89, is inserted in the screen grid circuit for test purposes as hereinafter described. The condenser 90 is a by-pass condenser lowering the plate circuit resistance. I

switch 89 is closed in normal position and shunts the resistor 88. When the button is pressed, this resistor is introduced in the screen circuit and changes suddenly-the value of the screen grid voltage, which in turn produces a sudden fluctuation in the plate current. The electric impulse is rectified by the rectifier 58 and produces a sudden deflection of the needle in the meter L. When the button is released the switch shunts the. resistor again and another impulse is produced in the meter. The same switch 92 closes thebattery N on both the filament ll of the battery and the lamp 60 shown in the diagram of connections, Fig. 16.

'Fig. 1'7 shows a longitudinal section through the detector I which is enclosed in a streamline shell composed of a cylindrical middle section 93 and two removable caps 96 and 95. The two halves of the doublet H enter the shell through the-insulators 96 and 91. A shielded cable 98 brings the power from-the batteries M and N through the junction .box K shown in Fig. 19. g

The detector housing is constructed waterand weather-proof for outdoor operation and is supported when installed by the bracket 99 provided with four rubber shock absorbers I00 to' take up the vibrations of the vehicle upon which it is mounted Fig. 20 shows how the detector is mounted 1m.- der the fuselage of'an airplane parallel to the longitudinal axis. The terminals of the antenna are supported by two small brackets Hill and H02 through the insulators l03'and Hit. This symmetrical installation is preferred although the device will operate as well if installed under the wings or elsewhere under the body of the aircraft. It cannot be installed, however, ,above the metallic structure of the aircraft because this structure will screen the energy of the beam from the receptor and no signal will be intercepted.

Figs. 8 and 9 illustrate a horizontal and vertical section through the fan-shaped beam produced by the projector P and the displacement of the receptor R through the beam in a typical blind landing operation of an airplane Q. The

contour S represents the loci of points in space having a field strength suflicient to operate the indicator and flash the signal on the airplane if the receptor is provided with a non-directional antenna. This beam has been found in actual practice to be too broad. I have associated, therefore, with the receptor a directional antenna H of the doublet type which is installed parallel to the direction of flight of the airplane .Q.

In the landing process the line of approach of the airplane is known in advance and'the projector P is disposed on the ground so that its doublet antenna is also arranged parallel to the line of flight. The airplane, therefore, displaces the receptor antenna parallel to the projector real beam S in the direction of flight and which has a greater. lateral spread. In other words,

on account of the directional characteristic of the receiving antenna the airplane penetrates deep into the beam before a sufiicient electro'motive force is induced in the receiving antenna to actuate the flasher.

It is obvious, therefore, that by relative and predetermined displacements of the transmitting and receiving directional antennae I can modify at will the shape of any beam and realize on an aircraft efiects of virtual beams which have considerable value as an aid to navigation inpoor visibility.

During the landing operation, the pilot has to watch many other instruments and knowledge of his position with respect to the boundary of the field should be brought to him not only with great precision but the signal must be also of such nature that it willnot escape the notice of the pilot no matterhow busy he is watching and interpreting other flight instruments. Of particular importance is the proper position at which he should start the glide into the landing field. Another important position is the boundary of the landing area and also the center of this area.

Taking into consideration these conditions, I have provided the indicator L with a powerful light bulb, which is capable of attracting the attention of the pilot even if he is not looking at the instrument the moment it is actuated by the signal.

As it can be judged from the above description, the equipment used either on the ground or on the vehicle is light, simple and'economical. It occupies little space and cannot be disturbed by static or distant stray radiations. The projector also has a limited range and the energy being projected upwards will not produce any'interference with ultra-short wave receivers operating on the same frequency in the same area.

The operation of the receptor on the aircraft is also very simple. The only operation required from the pilot before using the device is to throw in the filament switch 92 and to check the operation by pressing the button 9! on the test switch 89, as already explained.

I claim;

1. In a system for generating and projecting radiant energy of ultra-highfrequency in a substantially vertical direction with respect to an aircraft landing field, antenna means, reflecting means associated with said antenna means and parallelly spaced therefrom substantially onequarter wave length of the radiated energy, means for generating said energy and for transferring the same to said antenna means at a point of substantially minimum potential thereof for projection above the landing field, and means disposed adjacent said antenna means for neutralizing certain undesired radiation components.

2. In a system for generating and projecting radiant energy of ultra-high frequency in a substantially vertical direction with respect to an aircraft landing field, antenna means, reflecting means associated with said antenna means and parallelly spaced therefrom substantially onequarter wave length of the radiated energy. means for generating said energy and for transferring the same to said antenna means, said generating and transferring means being disposed within the field of radiated energy and shielding means for said generator to prevent stray radiation of the generated energy from interfering with the radiation from said antenna means and aiaasae vent interference between the respective fields of operating to neutralize certain undesired radiation components of the projected energy from said antenna means whereby the projection of energy is effected in a relatively narrow zone in a plane normal to the axis oi. said antenna means.

3. In a system for generating and projecting radiant energy of ultra-high frequency in a substantially vertical direction with respect to an aircraft landing field, antenna means, reflecting means associated with said antenna means, and parallelly spaced therefrom a distance equivalent to substantially one-quarter wave length of the radiated energy, means for generating said energy and for transferring the same to said antenna at a point of substantially minimum potential, said generating and transferring means being symmetrically coupled withrespect to the nodal point of said antenna, and means disposed adjacent said antenna means for neutralizing certain undesired radiation components whereby radiation of energy is efiected in a relatively narrow zone in a plane substantially normal to the axis of said antenna means.

4. In a system for generating and projecting radiant energy of ultra-high frequency, antenna means, reflecting means associated with said antenna means and parallelly spaced therefrom a distance equivalent to substantially one-quarter wave length of the radiated energy, means for generating said energy and for transferring the same to said antenna at a point of substantially minimum potential, said generating and transferring means being arranged symmetrically with respect to and substantially at the nodal point of said antenna means, and a metallic shield enclosing said generating and transferring means and electrically coupled to said antenna and operating to neutralize certain of the radiation components whereby radiation from said antenna -means is effected in a relatively narrow zone in a plane substantially normal to the axis of said antenna means. r

5. In a system for generating and projecting radiant energy of ultra-high frequency in a substantially vertical direction with respect to an aircraft landing field, antenna means including a doublet and a reflecting means, an ultra-high frequency generator connected with said antenna means, and means suitably spaced from and dis: posed in symmetrical relation with said doublet for shaping the projected beam in a confined zone extending in a plane substantially normal to the axis of said doublet. a K

6. Means for projecting a beam of ultra-high frequency radiant energy comprising a doublet having a pair of spaced but aligned sections, an ultra-high frequency generating circuit coupled to and disposed approximately at the nodal point of said doublet and between the aligned sections thereof and shielding'means for said circuit extending around the spaced adjacent ends of said doublet and operating to prevent interference between the respective flelds of said doublet and said circuit.

7. Means for projecting a beam of ultra-high frequency radiant energy comprising a doublet having a pair ofspaced but aligned sections, an ultra-high frequency oscillating circuit coupled to and disposed approximately at the nodal point of said doublet and located between the adjacent ends of the sections of said doublet, a source of power associated. with said circuit and a metallic shield capacitively coupled to said doublet and enclosing said circuit and operating to presaid doublet and said circuit.

8. Means for projecting a beam of ultra-high frequency radiant energy comprising a doublet, an ultra-high frequency oscillating circuit coupled to and disposed approximately at the nodal point of said doublet, a source of power associated with said circuit and a metallic shield capacitively coupled to said doublet at approximately its nodal point to constitute a part thereof, and enclosing said circuit and operating to prevent interference between respective fields of said doublet and said circuit.

9. Means for projecting a beam of ultra-high frequency radiant energy comprising a doublet, an ultra-high frequency oscillating circuit coupled to and disposed approximately at the nodal point of said doublet, a source of power associated with said circuit and a support for said doublet and the oscillating circuit coupled therewith comprising a metallic shield capacitively coupled to said doublet and enclosing said circult and operating to prevent interference between the respective fields of said antenna and said circuit. a

10. Means for projecting a beam of ultrahigh frequency radiant energy comprising a doublet, an ultra-high frequency oscillating circuit symmetrically coupled to and disposed approximately at the nodal point of said doublet, a source of power associated with said circuit and a pedestallike support for said doublet comprising a metallic shield capacitively coupled to said doublet and enclosing said circuit and operating'to prevent interference between the respective iields of said antenna and said circuit.

11. In a system for receiving high frequency radiant energy, a substantially tubular casing adapted to be suspended from an aircraft, a removable closure for' each end of said casing, and a doublet antenna having a pair of sections disposed in alignment with each other, the sections being carried by the respective removable end closures and projecting in opposite directions from said casing, and a detector device within said casing having the elements thereof extending substantially in alignment with the direction of axis of said sections.

12. In a system for receiving high frequency radiant energy, a high frequency radio receiver,

' tions, one of said sections being carried by each of said end caps, and means for establishing connection between the radio receivingapparatus in said casing and the sections of said doublet when said end caps carrying the sections of said doublet are mounted in position.

'13. In a system for receiving high frequency radiant energy, a radio receiver casing adapted to be mounted on an aircraft, a'radio receiver carried within said casing, a streamline closure member adapted to fit over each end of said casing, and a doublet antenna comprising a pair oi aligned sections, one of said sections being carried by each of said streamline closure members, and connections between the radio receiving apparatus within said casing and the sections of said doublet antenna.

14. In a system for receiving high frequency radiant energy, a substantially tubular casing adapted to be suspended from an aircraft, a etreamline closure for each end of said casing, and a doublet antenna having a pair of sections disposed-in alignment with each other, the sections being carried by the respective streamline end closures and projecting in opposite directions tending axially in opposite directions therefrom,

a pair of streamline closure members adapted to engage opposite ends of said tubular casing, and a doublet antenna having aligned sections, one of said sections being carried by one of. said streamline closure members and the other of said sections being carried by the other of said streamline closure members, each of said sections terminating in a socket adapted to be engaged with said connecting means when said streamline closure members are engaged with said tubular casing.

16. In combination with a projector of ultrahigh frequency energy generating in space a fanshaped beam thrown across the path of an airplane flying or landing in conditions of poor visibility, substantially horizontal directive antennae installed under an aircraft and substantially parallel to the longitudinal axis thereof, detecting means .connected with said antennae, and indicating means cooperating with said detecting means for indicating to a pilot the position of theaircraft with respect to the location of said fan-shaped beam.

1'1. In combination with a projector of ultrahigh frequency energy generating in space a vertical beam and comprising as a radiator a substantially horizontal doublet spaced substantially a quarter wave above the ground or any horizontal reflecting conducting surface, detecting means on an aircraft associated with a substantially horizontal directive antenna installed under the structure of the aircraft and substantially parallel to the longitudinal axis of the aircraft,

and indicating means cooperating with said detecting means to indicate to the navigator the location of the aircraft when the said aircraft is flown through the vertical beam in conditions of poor visibility with the axis of the antenna on the aircraft aligned with the axis of thedoublet on the ground or adjacent said reflecting conducting surface. p

18. In a system of blind landing of aircraft in combination with a detector. of ultra-high frequency energy, a substantially horizontal antenna installed under the structure of an aircraft substantially parallel to its longitudinal axis, a similar antenna located on the ground and adapted to be continuously excited with ultrahigh frequency energy for establishing a high frequency field of force substantially normal to the path of flight of the aircraft, the antenna on the aircraft being substantially alignable with the antenna on the ground by maneuvering the aircraft, and indicating means cooperating with said detecting means to indicate to the pilot the passage of the aircraft through the high frequency field established by the antenna on the ground. 19. In a landing system for aircraft in combination, a doublet directive transmitter for propagating a field of high-frequency energy vertically upward from a position adjacent a landing fleld in a plane substantially normal to the path of flight of an aircraft, and a doublet antenna carried by anaircraft having the elements of said doublet extendingsubstantially parallel with the amazes longitudinal axis of the aircraft for intercepting said propagated energy and an indicator on the aircraft actuated by energy received by said last mentioned doublet antenna. 1

20. In a blind landing system for aircraft which includes means for establishing high-frequency beams of energy for denoting location of aircraft with respect to the ground, a receiving system carried by aircraft and adapted to intercept established high frequency beams of energy, comprising an antenna, an electron tube device including a cathode, acontrol grid, an anode and a screen grid electrode, means for supplying operating potentials to said electrodes, an input with respect .to the ground, a receiving system) carried by aircraft and adapted to intercept established high-frequency beams of energy, comprising an antenna, an electron tube device including a cathode, a control grid, an anode and a screen grid electrode, means for supplying operating potentials to said electrodes, an input circuit connecting certain of said electrodes with said antenna, a flash indicator, an output circuit connecting certain of said electrodes with said flash indicator, and means for modifying the potential supplied to saidoscreen grid electrode for producing a change in current flow in said output circuit for operating said flash indicator independently of the interception of high-frequency energy by said antenna.

22. In a blind landing system for aircraft which includes means for establishing high-frequency 'beams of energy for denoting location of aircraft with respect to the ground, a receiving system carried by aircraft adapted to intercept established high-frequency beams of energy, comprising an antenna, an electron tube device including a 'cathode, a control grid, an anode and a screen grid electrode, means for supplying operating potentials to said electrodes, an input circuit connecting certain of said electrodeswith said antenna, a flash indicator, an output circuit connecting certain of said electrodes with said flash. indicator, and means for abruptly changing the potential applied to said screen grid electrode for producing a current impulse in said output circuit for operating said flash indicator independently of the interception of high-frequency energy by said antenna.

23. In a blind landing system for aircraft which includes means for establishing high-frequency beams of energy for denotingtlocation of air- .craft with respect to the ground, a receiving system carried by aircraft adapted to intercept established high-frequency beams of energy, comprising an antenna, an electron tube device including a cathode, a control grid, an anode.

and a screen grid electrode, means for supplying operating potentials to said electrodes, an;

input circuit connecting certain of said electrodes with said antenna, a flash indicator, an output circuit connecting certain of said electrodes with said flash indicator, a resistor disposed in a series path with said screen grid and with said potential supply means, a switch normally shunting said resistor for allowing normal operation of said electron tube device, said switch being movable to open position for introducing said resistor efiectively in said series path and modifying the potential on said screen grid ior producing a current fluctuation in said output circuit suificient to actuate said flash indicator independently of the interception of high-frequency energy by said antenna.

24. In a blind landing system for aircraft which includes means for establishing high-frequency beams of energy for denoting location of aircraft with respect to the ground, a receiving system carried byaircraft adapted to intercept established high-frequency beams of energy, comprising an antenna, an electron tube device including a "cathode, a control grid, an anode and a screen grid electrode, means for supplying operating potentials to said electrodes, an input circuit connecting certain of said electrodes with said antenna, a flash indicator, an output circuit connecting certain of said eiectrodes with said flash indicator, and means for abruptly decreasingthe current flow to said screen grid for instantaneously increasing the current flow in said output circuit for actuating said flash indicator independently of the interception of highfrequency energy by said antenna.

25. An aircraftreceiver for ultra-high-frequency energy comprising a streamline casing adapted to be mounted substantially parallel with the longitudinal axis of an aircraft, a doublet antenna having opposite sections thereof projectlng from opposite ends of said streamline casing, and signal receiving apparatus housed within said streamline casing, and electrically connected with the opposite sections of said doublet antenna, a radiating system on the ground comprising a transmitter with a doublet antenna -connected thereto extending in a direction for establishing a field of high frequency energy in a plane substantially normal to the path of flight of the aircraft, whereby the doublet antenna on the aircraft may be substantially aligned with the doublet antenna on the ground for receiving energy from the field of high-frequency energy established by the doublet antenna on the ground for actuating said signal receiving apparatus and indicating the position of the aircraft.

CONSTANTIN D. BARBULESCO. 

